Casey Anthony stands in the courtroom with her defense attorney Jose Baez (l.) as the jury enters during her trial at the Orange County Courthouse on Monday, June 13, in Orlando, Fla. Anthony is charged with killing her 2-year-old daughter in 2008.

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An FBI fingerprint expert testified on Monday in an Orlando murder trial that she noticed a heart-shaped outline on a piece of duct tape that prosecutors say was used by a Florida mother to smother her 2-year-old daughter.

Elizabeth Fontaine, a forensic examiner in the Federal Bureau of Investigation’s latent print unit, told the jury that she noticed the heart-shaped object while using ultraviolet light to inspect the duct tape for possible fingerprints.

“If you were to wear a band-aid for an extended period of time you have that glue and debris outline,” she said. “Rather than a band-aid it is in the shape of a heart.”

In a strange twist, the heart-shaped outline mysteriously disappeared from the duct tape before forensic experts were able to photograph it.

Analysts have speculated that the outline was caused by a small heart-shaped sticker. The presence of a heart-shaped sticker on the duct tape would be important because prosecutors contend that the heavy-duty tape was the murder weapon used by Casey Anthony to kill her daughter Caylee in June 2008.

Ms. Anthony is charged with first-degree murder. She allegedly drugged her daughter with chloroform, suffocated her by affixing three pieces of duct tape 6 to 8 inches long over her nose and mouth, hid the body in the trunk of her car for several days, and then dumped it in a wooded area not far from the family home.

Anthony failed to notify police, her family, or friends of her missing daughter for 31 days. When confronted, she said the child had been kidnapped by a nanny.

Anthony has pleaded not guilty. Her lawyers say Caylee died accidentally in the family’s swimming pool.

Fontaine’s appearance came as the state is preparing to wrap up its case perhaps as early as Tuesday afternoon after three weeks of testimony.

The state is expected to try to connect Fontaine’s testimony concerning the heart-shaped outline with sheets of heart-shaped stickers investigators found during a search of the Anthony home. The search was conducted shortly after Caylee’s skeletal remains – and the pieces of duct tape – were discovered on Dec. 11, 2008, six months after the toddler’s disappearance. By then, Anthony was the prime suspect in a murder investigation.

In a potential setback for prosecutors, Fontaine testified that she did not photograph the heart-shaped outline or otherwise preserve the evidence at the time she first observed it. Instead, she continued conducting tests to try to identify fingerprints on the tape. (No prints were found.)

Fontaine told the jury that when she went back to photograph and record the apparent heart-shaped piece of evidence it was no longer visible.

It is unclear how members of the jury may view that lack of documentation by the nation’s premier crime laboratory. Fontaine’s testimony about the heart-shaped outline was based on her personal observation and her case notes.

Judge Belvin Perry told the jury that the trial is running ahead of schedule. He said prosecutors may rest their case on Tuesday or early Wednesday; the defense may begin its case as early as Wednesday afternoon.

Jury deliberations could begin on June 25 or June 27, Judge Perry said.